1. Field of the Invention
This invention is concerned with a method for the selective preparation of 3,4-dimethyl-1-ethylbenzene from xylene and ethylene utilizing a shape selective zeolite catalyst.
2. Description of the Prior Art
Six structural isomers of the compound dimethylethylbenzene are known to exist. The names, structures, boiling points and equilibrium distribution at 315.degree. C. of these isomers are as shown below in Table I.
TABLE I ______________________________________ Boiling Equilibrium % Name and Structure Point, .degree.C. at 315.degree. C.* ______________________________________ 2,3-Dimethyl-1-ethylbenzene 193.9 3.2 ##STR1## 2,4-Dimethyl-1-ethylbenzene 188.4 16.4 ##STR2## 2,5-Dimethyl-1-ethylbenzene 186.9 23.9 ##STR3## 2,6-Dimethyl-1-ethylbenzene 190.0 1.9 ##STR4## 3,4-Dimethyl-1-ethylbenzene 189.8 20.9 ##STR5## 3,5-Dimethyl-1-ethylbenzene 183.8 33.7 ##STR6## ______________________________________ *S. Csicsery, J. of Catalysis, 19, 394 (1970)
A process for the synthetic manufacture of these compounds via ethylation of xylene or of mixed xylenes in the presence of aluminum chloride is disclosed in U.S. Pat. No. 3,855,331 to Moss et al. However, the data disclosed therein demonstrates that even at low temperatures alkylation is not selective for any particular isomer of dimethylethylbenzene. Other literature on the transalkylation of 2-ethyltoluene on H-Mordenite [S. Osicsery, Journal of Catalysis, 23, 124 (1971)] indicates that this zeolite is not particularly shape selective for the production of 3,4-dimethyl-1-ethylbenzene, yielding only 30% to 50% at between 200.degree. C. and 300.degree. C.
3,4-Dimethyl-1-ethylbenzene is an intermediate useful for the production of 3,4-dimethylstyrene. A process for the selective production of 3,4-dimethyl-1-ethylbenzene would eliminate the expense and waste of presently employed processes for isolating this isomer from equilibrium mixtures of the various dimethylethylbenzenes.